The invention relates to a process for determining 3-D data of at least one prepared jaw area such as a prepared tooth stump by mechanical scanning of the jaw area and digitizing the measured values determined during the scanning.
A process for the production of a denture consisting of ceramic material can be gathered from EP-A-0 580 565. In it, a prepared tooth in the mouth of a patient can be optically or mechanically photographed in order to then produce the denture from the values determined in this manner and digitized by a milling machine.
Other processes provide that an impression is taken of the prepared jaw area, in particular a tooth stump, in order to produce a positive model that is scanned and digitized (EP-B-1 067 880).
All processes, whether a direct scanning in the patient's mouth, or a scanning of an impression require a completely or almost completely prepared jaw area in order to obtain the desired 3D data. In the case of a partially defective impression or not completely scanned jaw area there is then the possibility, as a function of the software used, of supplementing missing data or of removing obviously inappropriate data in order to avoid that the denture produced is defective.
The present invention is based on the problem of further developing a process of the initially cited type in such a manner that the 3-D data required for the production of the denture can be determined without expensive scanning processes or the production of a positive model being necessary.
In order to solve the problem the invention substantially provides that the jaw area, such as a tooth stump, to be prepared is prepared with a dental instrument whose positions are optically measured during the preparation and that the 3-D data is determined from the positions of the dental instrument that are associated with the prepared jaw area. The positional data of the dental instrument during the preparation of the jaw area is used for the determination of the final contour of the prepared jaw area. Therefore, it is not necessary that the jaw area is at first prepared and is subsequently scanned with a separate apparatus. This is time-consuming and expensive on account of the various apparatuses used. In contrast thereto, according to the invention the jaw area is tactilely scanned simultaneously with the preparation of the jaw area in order to make the required digitized measured values available after the conclusion of the preparation in order to be able to make a denture.
In order to make possible the determination of the position of the dental instrument, it is provided with optically effective markings that are detected by an optical sensor for the spatial determination of the position of the dental instrument. In particular, the dental instrument is a drill for preparing the jaw area.
In general, the dental instrument should consist of a handle such as a hand grip and of a replaceable insert such as, e.g., a drill. The handle should have markings so that one and the same handle can be used for different inserts or tools.
When an insert is replaced the different effective geometry of the inserts must be taken into account and a calibration is to be carried out.
In order to ensure an unambiguous determination of the position and therewith of the geometry, it is furthermore provided that the dental instrument is calibrated before the preparation by scanning a normal such as a sphere. These types of measures are sufficiently known from the technology for measuring coordinates in conjunction with the tactile measuring of workpieces so that these previously known measures are referred to and reference is explicitly made to them.
A further development of the invention that is to be emphasized provides that the positions of the dental instrument are determined taking into consideration any movement of the jaw area. In other words, the movement data of the dental instrument is offset against the movement data of the jaw in order to be able to calculate the 3-D data record.
To this end a position sensor arranged stationarily relative to the jaw area can be associated with the jaw area. The position sensor can comprise optically effective markings stationarily associated with the jaw area and can comprise an optical sensor that detects the movement of the markings. However, an inertial platform can also be used for determining positions whose data is offset with that of the optical sensor, by means of which the movements of the dental instrument are detected.
In particular, light sources such as LEDs or optical reflectors are used for the first and/or second optically effective markings. In the latter instance it is necessary that the reflectors are loaded with light in order to be able to detect the reflected light with the optical sensor such as a camera.
The 3-D data corresponding to the prepared jaw area is then processed in order to produce a denture by a software, in particular CAD software, which denture can fit on the jaw area, in order to then produce the desired denture by a CAM program from a blank, in particular consisting of porous and pre-sintered ceramic material. This basically takes place by milling. However, the denture can alternatively also be produced on the basis of the 3-D data in a building-up process such as rapid prototyping.
A further embodiment of the invention to be emphasized provides that the inner contour of the denture is determined and calculated from the 3-D data determined by the positional determinations of the dental instrument and that the outer contour is determined and calculated from determined digitized data and/or data taken from a library from scanning the jaw area surrounding the jaw area to be provided with the denture.
The teaching of the invention, the working of the jaw area and the simultaneous determination of the final contour in a single process have the advantage that measuring uncertainties during touching present regarding tactile measuring do not occur. As regards intraoral scanners, there is the advantage that no preparation edge must be exposed because it is frequently required during contactless scanning that the gum on the preparation boundary is pressed away by a thread. Translucency of the tooth or liquid in the jaw area are not a problem during the determination of the contour. Problematic gingiva is pressed away by the dental instrument during the preparation.
In particular, a rotating tool such as a drill is used as dental instrument in which the receptacle or handle of the rotating tool has at least three optical markings such as light-emitting diodes that are detected by a receiver in order to detect the spatial position of the tool in this manner. Due to the ability of the rotating tool to be replaced, it is necessary when using a new rotating tool that a calibration or teaching takes place on a normal such as a reference sphere.
According to the invention an outline is formed during the preparation that corresponds to the form of the prepared jaw area such as a tooth stump. The movement of the patient is additionally considered in order to avoid measuring errors.
In particular, the process of the invention is used to produce caps, a frame or an inlay. An exceedingly precise determination of contour takes place.
In contrast to the above, it is basically not necessary to take into account a possible relative movement of the jaw area to be prepared to the jaw itself since the cutting forces occurring during the preparation are so small that distortions of the measured values are excluded.
In order to initiate a measuring procedure the cutting in of the tool or, e.g., a power change of the tool can be used that occurs when the drill comes in contact with the jaw area to be prepared and the working begins.
In the case of a drill as dental instrument the movement of a rotating tool guided by the preparing person such as a dentist is detected. In order to detect the movements of the drill several optical markings such as LEDs are applied on it or on its holder. The calibration of the tip of the rotating tool to the optical marking takes place by touching a normal such as a reference sphere at several positions.
In order to detect the movement of the jaw a platform with at least three optical markings or an inertial platform is stationarily connected to the jaw. The sensor detecting the jaw movement can be fastened on a face leading to the jaw or in a bite block arranged between the lower and the upper jaw. The jaw movement can be detected by the optical sensor that determines the movement of the dental instrument. However, a separate sensor can also be used that stands in a stationary relationship to the optical sensor for the dental instrument.
In order to also digitize areas that are not prepared, it is provided that the dental instrument scans the areas of the jaw area such as at least one tooth and if required necessary parts of the jaw ridge, which areas are not provided for working in the course of the treatment phase. This yields data that can be used for the calculation of the outer contour of a denture to be produced.
Independently of the above, a further development provides that the preparation boundary is determined with a separate feeler or with an insert such as a feeler pin which insert can be provided with a dental instrument or its handle.
According to the invention a dental instrument used to prepare a jaw area is used at the same time as an oral scanner.
Further details, advantages and features of the invention result not only from the claims, the features to be gathered from them whether alone and/or in combination but also from the following description of preferred exemplary embodiments to be gathered from the drawings.